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Impact of the CO2 and H2O clouds of the Martian polar hood on the polar energy balanceClouds covering extensive areas above the martian polar caps have regularly been observed during the fall and winter seasons of each hemisphere. These 'polar hoods' are thought to be made of H2O and CO2. In particular, the very cold temperatures observed during the polar night by Viking and Mariner 9 around both poles have been identified as CO2 clouds and several models, including GCM, have indicated that the CO2 can condense in the atmosphere at all polar latitudes. Estimating the impact of the polar hood clouds on the energy balance of the polar regions is necessary to model the CO2 cycle and address puzzling problems like the polar caps assymetry. For example, by altering the thermal radiation emitted to space, CO2 clouds alter the amount of CO2 that condenses during the fall and winter season. The complete set of Viking IRTM data was analyzed to define the spatial and temporal properties of the polar hoods, and how their presence affects the energy radiated by the atmosphere/caps system to space was estimated. The IRTM observations provide good spatial and temporal converage of both polar regions during fall, winter, and spring, when a combination of the first and the second Viking year is used. Only the IRTM brightness temperatures at 11, 15, and 20 microns are reliable at martian polar temperatures. To recover the integrated thermal fluxes from the IRTM data, a simple model of the polar hood, thought to consist of 'warm' H2O clouds lying above colder and opaque CO2 clouds was developed. Such a model is based on the analysis of the IRIS spectra, and is consistent with the IRTM data used.
Document ID
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Forget, Francois
(NASA Ames Research Center Moffett Field, CA, United States)
Pollack, James B.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1993
Publication Information
Publication: Lunar and Planetary Inst., Workshop on Atmospheric Transport on Mars
Subject Category
Lunar And Planetary Exploration
Accession Number
Distribution Limits
Work of the US Gov. Public Use Permitted.

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